Fiber optic cable assembly with overlapping bundled strength members, and fabrication method and apparatus

ABSTRACT

A fiber optic cable assembly includes first and second cable sections each having a jacket, at least one optical fiber, and multiple strength members. An intermediate cable section includes at least one splice joint as well as bundled sections of strength members of the cable sections formed into bundled sections that overlap and are adhered together. As adhered, the bundled strength members are shorter than the at least one spliced optical fiber in the intermediate section to ensure that the strength members bear tensile loads. A fabrication method includes binding unjacketed segments of strength members of two cable sections into bundled sections of strength members, fusion splicing ends of optical fibers, polymerically overcoating at least one splice joint, and adhering the bundled sections of strength members in an overlapping arrangement. An apparatus for thermoplastically coating cable assembly portions includes a trough for molten thermoplastic material, and a lateral insertion slot defined therein.

BACKGROUND

This application is a divisional of U.S. application Ser. No.16/940,476, filed on Jul. 28, 2020, which claims the benefit of priorityto U.S. Application No. 62/880,757, filed on Jul. 31, 2019, bothapplications being incorporated herein by reference.

BACKGROUND

The disclosure relates generally to fiber optic cables incorporatingtensile strength members and protected fusion splices, in addition tomethods and apparatuses for fabricating such cables.

Optical fibers are useful in a wide variety of applications, includingthe telecommunications industry for voice, video, and data transmission.In a telecommunications system that uses optical fibers, there aretypically many locations where fiber optic cables, which carry theoptical fibers, connect to equipment or other fiber optic cables. Fiberoptic cables are frequently produced by extruding thermoplastic material(e.g., polyvinylchloride (PVC)) over at least one coated optical fiber.

FIG. 1 is a cross-sectional view of an exemplary coated optical fiber 10that includes a glass core 12, glass cladding 14 surrounding the glasscore 12, and a polymer coating 20 (wherein may include multiple coatinglayers, such as an inner primary coating layer 16 and an outer secondarycoating layer 18) surrounding the glass cladding 14. The inner primarycoating layer 16 may be configured to act as a shock absorber tominimize attenuation caused by any micro-bending of the coated opticalfiber 10. The outer secondary coating layer 18 may be configured toprotect the inner primary coating layer 16 against mechanical damage,and to act as a barrier to lateral forces. The outer diameter of thecoated optical fiber 10 may be about 200 μm, about 250 μm, or any othersuitable value. Optionally, an ink layer (e.g., having a thickness ofabout 5 μm) may be arranged over the outer secondary coating layer 18 ofthe coated optical fiber 10 to color the fiber (e.g., as is commonlyused in ribbonized fibers), or a coloring agent may be mixed with thecoating material that forms the outer secondary coating layer 18. Anadditional buffer coating (“buffer”; not shown), may be applied to thecoated optical fiber 10 to provide additional protection and allow foreasier handling, effectively forming a cable. The buffer may be embodiedin a layer of different material applied to the coating 20, therebyforming a “tight buffer” closely surrounding (intimately contacting andconforming to) the coating 20. Alternatively, the buffer may be embodiedin a pre-formed tube (also known as a furcation tube or buffer tube)that has an inner diameter larger than the coating 20 and into which thecoated optical fiber 10 is inserted, thereby forming a “loose buffer.”This additional buffer typically has an outer diameter of about 900 μm.

In this disclosure, the term “optical fiber” (or “fiber”) will be usedin a generic sense and may encompass bare optical fibers, coated opticalfibers, or buffered optical fibers, as well as optical fibers includingdifferent sections corresponding to these fiber types, unless it isclear from the context which of the types is intended. “Bare opticalfibers” (including “bare glass optical fibers”) or “bare sections” arethose with no coating present on the fiber cladding. “Coated opticalfibers” or “coated sections” include a single or multi-layer coating(typically an acrylic material) surrounding the fiber cladding and havea nominal (i.e., stated) diameter no greater than twice the nominaldiameter of the bare optical fiber. “Buffered optical fibers” or“buffered sections” are coated optical fibers with an additional bufferthat increases the nominal diameter of the optical fiber to more thantwice the nominal diameter of the bare optical fiber, with 900 μm beingthe most typical nominal diameter. Buffered optical fibers may also bereferred to as “buffered cables.” Finally, the term “unbuffered opticalfibers” refers to optical fibers without a buffer, and therefore mayencompass either bare optical fibers or coated optical fibers.

Optical fiber fusion splicing, which is the process by which apermanent, low-loss, high-strength, fused (or welded) joint is formedbetween two optical fibers, typically involves multiple tasks. First,polymer coatings (e.g., coating layers 16, 18 of FIG. 1 ) of coatedoptical fibers (e.g., coated optical fiber 10 of FIG. 1 ) are strippedto expose glass cladding (e.g., glass cladding 14 of FIG. 1 ). Next,flat fiber end faces are formed, typically by cleaving exposed glassportions of the fibers. Then the fibers are laterally aligned to eachother. The fiber tips must be heated to their softening point andpressed together to form a joint. Checks such as loss estimation andproof testing (to ensure long-term mechanical reliability) may beperformed. The completed fusion splice must also be protected from theenvironment using packaging, which serves to shield fiber surfaces frommechanical degradation (e.g., abrasion) and chemical degradation (e.g.,humidity) to ensure that splices exhibit long-term reliability. Opticalfibers must typically be able to withstand service temperatures spanningat least a range of from −40° C. to 85° C. without suffering significantmechanical and/or optical performance degradation.

Fusion spliced optical fibers are typically used in modules andenclosures in which virtually no mechanical force is applied to thefiber splices. When used in cable assemblies in which fiber optic cablesare subject to bending and tensile loads during installation andpossibly during operation, an external housing is typically utilized tocontain the splices, and strain relief or strength members of the cablesare mechanically coupled to the housing. Typically, strength membersconsist of aramid yarn (e.g., Kevlar), and can be attached to a housingby a threaded interconnect, a crimp connection, or epoxy adhesive. Thepresence of a housing with strength members coupled thereto andcontaining fusion splices invariably increases the size anddetrimentally impacts the aesthetics of spliced fiber optic cables.

U.S. Pat. No. 8,696,221 B2 discloses a method for attaching a strainrelief member of a first cable to an outer jacket of the second cableusing a heat shrink splice protection sleeve configured to protect anoptic fiber splice. However, this method has limited utility since acable jacket is not an ideal strain relief material as it provideslimited load bearing capability, and presence of a comparatively largesplice protection sleeve is still required.

Heat shrink splice protection sleeves are commonly used as packaging toprotect spliced optical fibers. Such a sleeve may include an outer heatshrink tube (typically made of a heat shrinkable material (e.g., apolyolefin) and/or a non-stick material (e.g., polytetrafluoroethylene(PTFE)), an inner thermoplastic tube typically made of a melt flowadhesive material (e.g., ethylene vinyl acetate (EVA)), optionally incombination with a rigid (e.g., stainless steel) rod serving as asplint. When heated in an oven (e.g., associated with a fusion splicingtool), a thermoplastic tube melts and is compressed around the fiber andthe rigid rod by the heat shrink tube, forming a hermetic seal aroundthe fusion splice region.

An exemplary heat shrink protection sleeve 30 used to protect a splicejoint 32 formed between two coated optical fibers 10A, 10B isschematically illustrated in FIGS. 2A and 2B. The heat shrink protectionsleeve 30 includes a generally cylindrical inner tube 34 (e.g., a meltflow adhesive material such as ethylene vinyl acetate (EVA)) and agenerally cylindrical outer tube 36 (e.g., a polyolefin and/or PTFE),wherein the outer tube 36 generally surrounds the inner tube 34, and theinner tube 34 defines an interior passage 40. Although not shown, theinner tube 34 may optionally include a rigid rod useable as a splint.The outer tube 36 is required for conventional heat shrink protectionsleeves because the melt flow adhesive material (e.g., EVA) has a veryhigh viscosity and a very low softening temperature (e.g., about 100°C.). The more temperature-resistant outer tube 36 is typicallyconsidered indispensable, particularly when the splice is intended foroperation over a high temperature range of up to about 85° C. In use,the heat shrink protection sleeve 30 is positioned over a fusion splicedsection of two optical fibers 10A, 10B. The fusion spliced sectionincludes the splice joint 32 arranged between (stripped) glass claddingsegments 14A, 14B of the respective optical fibers 10A, 10B. Uponapplication of heat (typically within an oven), the inner tube 34 meltsaround the optical fibers 10A, 10B, the glass cladding segments 14A,14B, and the splice joint 32. The outer tube 36, which includes acylindrical outer surface 38, may include some heat shrinking capabilityto help the adhesive distribute around the fused optical fibers 10A,10B.

Groups of coated optical fibers (e.g., 4, 8, 12, or 24 optical fibers)may be held together using a matrix material, intermittent inter-fiberbinders (“spiderwebs”), or tape to form “optical fiber ribbons” or“ribbonized optical fibers” to facilitate packaging within cables. Forexample, optical fiber ribbons are widely used in cables for highcapacity transmission systems. Some modern cables in large-scale datacenters or fiber-to-the-home networks may contain up to 3,456 opticalfibers, and cables having even higher optical fiber counts are underdevelopment. Optical fibers that form a ribbon are arranged in parallelin a linear (i.e., one-dimensional) array, with each fiber having adifferent color for ease of identification. FIG. 3 provides across-sectional view of a multi-fiber ribbon 42, which includes twelveoptical fibers 44A-44L and a matrix 46 encapsulating the optical fibers44A-44L. The optical fibers 44A-44L are substantially aligned with oneanother in a generally parallel configuration, preferably with anangular deviation of no more than one degree from true parallel at anyposition. Although twelve optical fibers 44A-44L are shown in themulti-fiber ribbon 42, it is to be appreciated that any suitable numberof multiple fibers (but preferably at least four fibers) may be employedto form optical fiber ribbons suitable for a particular use.

Mass fusion splicing is a high throughput technology for interconnectinga large number of fibers in a ribbon format. First and second segmentsof up to twelve fibers arranged in a linear array can be fusion splicedsimultaneously by mass fusion splicing. Since sequential formation oftwelve fusion splices using a traditional single fiber fusion splicingtechnique is very time consuming, the ability to fusion splice linearlyarrayed segments of up to twelve fibers simultaneously enables entireribbons to be spliced rapidly, thereby improving manufacturingthroughput. Mass fusion splicing also allows for potential materialsavings. It enables migration from common indoor distribution cableswith 900 μm fibers to smaller mini-distribution cables with 250 μm or200 μm fibers, which is more cost-effective.

Heat shrink protection sleeves similar to those outlined above have alsobeen applied to protect optical fiber ribbon splices, which includemultiple fusion splices between first and second arrays of paralleloptical fibers contained in first and second optical fiber ribbonsegments, respectively. In such a context, an integrated strength membertypically includes a flat surface to support the fusion spliced fiberarrays, a thermoplastic inner tube is melted around the spliced ribboncables and the integrated strength member, and a moretemperature-resistant outer tube encases the thermoplastic inner tube.The cross section of a typical ribbon splice protector is 4 mm×4.5 mm,and the length is about 40 mm. Such a splice protector is suitable forinterfacing with optical fiber ribbons, but not jacketed cables sincethe cross-sectional width of a ribbon-type splice protector is muchlarger than that of a jacketed cable.

For end uses requiring smaller cable widths, loose tube cables having around cross section with an outer diameter of 2 mm or 3 mm are commonlyemployed. Alternatively, a round cable may include a rollable opticalfiber ribbon, such as disclosed in U.S. Pat. No. 9,939,599 B2 (with thecontent of such patent being incorporated by reference herein). As notedin the foregoing patent, a rollable optical fiber ribbon includes aribbon body formed over flexible polymeric material such that aplurality of optical fibers are reversibly movable between a position inwhich the optical fibers are arranged in a one-dimensional array and aposition in which the optical fibers are arranged in a curved shape froma cross-sectional view.

Conventional mass fusion splice technology, as well as conventionalsplice protection technology, only supports one-dimensional arrays ofoptical fiber splices. For splicing of fibers of small diameter roundcables, it is necessary to ribbonize loose tube fibers or arrangerollable optical fiber ribbons in a one-dimensional array to permit massfusion splicing, and the mass fusion spliced one-dimensional array offibers is typically protected in a bulky heat shrink sleeve. FIG. 4illustrates a conventional cable assembly 50 incorporating first andsecond loose tube-type cables 52A, 52B bearing pre-coated loose opticalfibers 54A, 54B, with stripped sections thereof that are mass fusionspliced in a one-dimensional array in a fusion splice region 56 that isprotected by a conventional ribbon splice protector 60. The ribbonsplice protector 60 includes an outer heat shrink member 64 and an innerthermoplastic member 62 that surrounds the fusion splice region 56 aswell as stripped sections (not shown) of the loose optical fibers 54A,54B. As shown in FIG. 4 , the ribbon splice protector 60 has a muchlarger diameter or width than a diameter or width of each of the loosetube-type cables 52A, 52B. Moreover, the width of each one-dimensionalarray of optical fibers 54A, 54B proximate to the inner thermoplasticmember 62 is also greater than the diameter of each of the first andsecond loose tube-type cables 52A, 52B. The benefits of small roundcables are thus defeated if a cable assembly incorporating small roundcables involves a mass fusion splice connection. The size ofconventional one-dimensional array splice protection technology limitsthe practical attainment of higher fiber density in fiber optic modulesand cable assemblies.

FIG. 5 shows a segment of a fiber optic cable 68 including an opticalfiber 70 and strength members 76 (e.g., aramid yarn) surrounded by ajacket 78. The optical fiber 70 includes a pre-coated portion 72 and astripped portion 71 from which a coating has been removed, with thestripped portion 71 of the optical fiber 70 having a cleaved end 74suitable for fusion splicing to another optical fiber (not shown). Theconfiguration shown in FIG. 5 may be obtained by removing the jacket 78from a portion of the fiber optic cable 68, trimming of the strengthmembers 76 to a length shorter than the portion of the optical fiber 70,stripping a coating from the optical fiber 70 to yield the strippedportion 71, and cleaving the optical fiber 70 to yield the cleaved end74.

FIG. 6 schematically illustrates a spliced fiber optic cable 80including a housing 86 filled with epoxy 88 for securing strengthmembers 76A, 76B of two fiber optic cable segments 68A, 68B andprotecting a splice region 82 including a splice between optical fibersegments 70A, 70B of the fiber optic cable sections 68A, 68B. Each fiberoptic cable section 68A, 68B includes a jacket 78A,78B that contains anoptical fiber 70A, 70B and strength members 76A, 76B such as aramidyarn. The strength members 76A, 76B are typically trimmed to a shorterlength (relative to ends of the jackets 78A, 78B) than the correspondingoptical fibers 70A, 70B. The strength members 76A, 76B are attached tothe housing 86 by potting an entire cavity 87 of the housing 86 withepoxy 88. The potting process is cumbersome in that it requires sealingone end of the housing 86, it consumes a large amount of expensive epoxymaterial, and it requires a long time period to permit the epoxy 88 tobe set (i.e., hardened) before the housing 86 and the spliced fiberoptic cable 80 can be handled.

In view of the foregoing, a need remains in the art for fiber opticcable assemblies incorporating fusion splices and strength members toaddress the above-described and other limitations associated withconventional fiber optic cable assemblies, as well as associatedfabrication methods and apparatuses.

SUMMARY

Aspects of the present disclosure provide a fiber optic cable assemblyincluding first and second cable sections each having at least oneoptical fiber and multiple strength members in a jacket, with anintermediate cable section including at least one splice jointconnecting the at least one optical fiber of the first and second cablesections, with strength members of the respective cable sections beingbundled into bundled sections, and with the bundled sections of thefirst and section cable sections being adhered to one another in anoverlapping manner in the intermediate cable section. Such anarrangement permits mechanical coupling between strength members of thefirst and second cable sections without requiring a housing cavityfilled with epoxy to effectuate such coupling. A method for fabricatinga fiber optic cable assembly is also provided. The method includingbinding strength members of first and second cable sections intorespective first and second bundled sections of strength members, fusionsplicing ends of at least one optical fiber of each cable section in anintermediate cable section, forming a polymeric overcoating over atleast one splice joint resulting from the fusion splicing, and adheringthe first and second bundled sections to one another in an overlappingmanner in the intermediate cable section. An apparatus for applying athermoplastic coating over components of a fiber optic cable assembly isadditionally provided. The apparatus includes a trough for containingmolten thermoplastic material arranged above a heated working surface,with a lateral insertion slot bounded in part by the working surface influid communication with the trough cavity. Such an apparatus may beused for applying thermoplastic material over strength members to formbundled sections of strength members, for applying thermoplasticmaterial over fusion splice regions, and for effectuating adhesionbetween overlapping bundled sections of strength members.

In one embodiment of the disclosure, a fiber optic cable assembly isprovided. The fiber optic cable comprises a first cable sectionincluding at least one first optical fiber and a plurality of firststrength members within a first jacket, and a second cable sectionincluding at least one second optical fiber and a plurality of secondstrength members within a second jacket. The fiber optic cable assemblyfurther comprises and intermediate cable section arranged between thefirst and second cable sections and including at least one splice jointjoining ends of the at least one first optical fiber and the at leastone second optical fiber. The intermediate cable assembly furtherincludes a first bundled section of the plurality of first strengthmembers, and a second bundled section of the plurality of secondstrength members. In the intermediate cable assembly, the first bundledsection overlaps with, and is adhered to, the second bundled section.

In accordance with another embodiment of the disclosure, a method forfabricating a fiber optic cable assembly is provided. The methodcomprises processing a first cable section, including at least one firstoptical fiber and a plurality of first strength members within a firstjacket, to bind an unjacketed segment of the plurality of first strengthmembers into a first bundled section of the plurality of first strengthmembers. The method further comprises processing a second cable section,including at least one second optical fiber and a plurality of secondstrength members within a second jacket, to bind an unjacketed segmentof the plurality of second strength members into a second bundledsection of the plurality of second strength members. The methodadditionally comprises fusion splicing ends of the at least one firstoptical fiber and the at least one second optical fiber to form at leastone splice joint defining a splice region of the fiber optic cableassembly, wherein each of the at least one first optical fiber and theat least one second optical fiber comprises a stripped portion proximateto the at least one splice joint. The method further comprises forming apolymeric overcoating over the at least one splice joint and over thestripped portion of each of the at least one first optical fiber and theat least one second optical fiber. The method further comprisespositioning the first bundled section of the plurality of first strengthmembers and the second bundled section of the plurality of secondstrength members in an overlapping arrangement, and adhering theoverlapped first and second bundled sections to one another.

In accordance with another embodiment of the disclosure, an apparatusfor applying a thermoplastic coating over components of a fiber opticcable assembly is provided. The apparatus comprises a support memberdefining a working surface. The apparatus further comprises a trougharranged above the working surface and defining a trough cavityconfigured to retain a pool of molten thermoplastic material. The troughis bounded by a rear wall, a front wall, side walls, and the workingsurface, and wherein a lateral insertion slot extends (i) between theworking surface and the front wall and (ii) between the working surfaceand at least portions of the side walls, with the lateral insertion slotbeing in fluid communication with the trough cavity. The apparatusfurther comprises a heating element configured to heat at least theworking surface to maintain the pool of molten thermoplastic material ina molten state.

Additional features and advantages will be set forth in the detaileddescription that follows, and in part will be readily apparent to thoseskilled in the technical field of optical connectivity. It is to beunderstood that the foregoing general description, the followingdetailed description, and the accompanying drawings are merely exemplaryand intended to provide an overview or framework to understand thenature and character of the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding, and are incorporated in and constitute a part of thisspecification. The drawings illustrate one or more embodiment(s), andtogether with the description serve to explain principles and operationof the various embodiments. Features and attributes associated with anyof the embodiments shown or described may be applied to otherembodiments shown, described, or appreciated based on this disclosure.

FIG. 1 is a cross-sectional view of a conventional coated optical fiberthat may be subject to fusion splicing, prior to stripping of amulti-layer polymer coating from glass cladding.

FIG. 2A is a schematic perspective view of a conventional heat shrinkprotection sleeve used to protect a splice joint between two opticalfibers.

FIG. 2B is a schematic cross-sectional view of the heat shrinkprotection sleeve and optical fibers of FIG. 2A, with schematicillustration of the splice joint between stripped portions of the twooptical fibers.

FIG. 3 is a cross-sectional view of a conventional optical fiber ribbonincluding twelve optical fibers.

FIG. 4 is a side view illustration of segments of two small round-typefiber optic cables from which twelve loose fibers extend, with the loosefibers being spliced in a one-dimensional array and protected by aconventional multi-fiber heat shrink protection sleeve.

FIG. 5 is a schematic side view illustration of a conventional fiberoptic cable including an optical fiber and strength members surroundedby a jacket, with portions of the optical fiber and strength membersextending beyond the jacket.

FIG. 6 is schematic side view illustration of a conventional splicedfiber optic cable including a housing filled with epoxy for securingstrength members of two fiber optic cable segments and protecting asplice between optical fibers of the fiber optic cable segments.

FIG. 7A is a schematic side view illustration of a fiber optic cableassembly according to one embodiment during a fabrication step prior toaddition of a tubular covering member, the fiber optic cable assemblyincluding first and second cable sections and an intermediate cablesection containing an overcoated fusion spliced optical fiber as well asoverlapping and adhered bundled sections of strength members emanatingfrom the first and second cable sections.

FIG. 7B is a schematic side view illustration of a fiber optic cableassembly according to one embodiment substantially identical to that ofFIG. 7A, but with the addition of a tubular covering member to theintermediate cable section to cover the overcoated fusion splicedoptical fiber and the adhered bundled sections of strength members.

FIG. 7C is a magnified central portion of FIGS. 7A and 7B including theovercoated fusion spliced optical fiber.

FIG. 8A is a side view illustration of a fiber optic cable sectionincluding a jacket as well as multiple optical fibers and strengthmembers, with portions of the optical fibers and strength members beingexposed following removal and peeling back of split portions of thejacket.

FIG. 8B is a side view illustration of the fiber optic cable section ofFIG. 8A following separation of the strength members from the opticalfibers and addition of a binding material to form a bundled section ofthe strength members.

FIG. 8C is a side view illustration of two (i.e., first and second)fiber optic cable sections according to FIG. 8B during a step offabricating a fiber optic cable assembly, following fusion splicing ofends of stripped sections of the fiber optic cable sections, prior to astep of adhering bundled sections of strength members of the first andsecond fiber optic cable sections.

FIG. 8D is a side view illustration of the fusion spliced first andsecond fiber optic cable sections according to FIG. 8C during anotherstep of fabricating a fiber optic cable assembly, after overlapping andadhering the strength members of the first and second fiber optic cablesections, to yield an uncovered fiber optic cable assembly.

FIG. 8E is a side view illustration of the uncovered fiber optic cableassembly of FIG. 8D arranged proximate to a metric ruler to show alength of an intermediate cable section arranged between jacketedportions of the first and second fiber optic cable sections.

FIG. 8F is a side view illustration of the fusion spliced first andsecond fiber optic cable sections of FIGS. 8D and 8E following thepositioning of a tubular covering member to surround the intermediatecable section as well as portions of the jackets of the first and secondfiber optic cable sections, with a metric ruler in the foreground toshow a length of the tubular covering member.

FIG. 9A is an upper perspective view illustration of a bare, mass fusionspliced section of two multi-fiber ribbon segments forming a splicedribbon cable, with a first lateral edge portion of the spliced ribboncable submerged in a pool of molten thermoplastic material atop asubstantially level, flat heated surface, and with the ribbon cablebeing tilted at an approximately forty-five degree angle relative to theflat heated surface during a ribbon insertion step, such that a secondlateral edge portion of the spliced ribbon cable is arranged at a levelabove the first lateral edge portion.

FIG. 9B illustrates the items of FIG. 9A, with the entire mass fusionspliced section of the spliced ribbon cable disposed in the pool ofmolten thermoplastic material atop the substantially level, flat heatedsurface, and with the first lateral edge portion being arranged atsubstantially the same horizontal level as the second lateral edgeportion of the spliced ribbon cable.

FIG. 10A is a perspective view of a portion of a fiber optic cablesubassembly during fabrication, showing a one-dimensional array oftwelve fusion spliced optical fibers, following adhesive binding ofpre-coated sections of the fusion spliced optical fibers to maintainpositioning of optical fibers in preparation for thermoplasticovercoating.

FIG. 10B is a perspective view of a fiber portion of a fiber optic cableassembly incorporating the subassembly of FIG. 10A, following additionof polymeric overcoating material that extends over stripped sections ofthe fusion spliced optical fibers, the splice region, and portions ofthe adhesively bound pre-coated sections.

FIG. 11A is a perspective view of a portion of a fiber optic cable withnon-coplanar groups of fusion spliced optical fibers that form a 2×6array, and overcoating material that extends over stripped sections ofthe fusion spliced optical fibers and the splice region.

FIG. 11B is a cross-sectional view of the fiber optic cable of FIG. 11A.

FIG. 12 is a perspective view of a portion of a fiber optic cablesubassembly during fabrication, showing a two-dimensional array ofmultiple fusion spliced optical fibers in a process of being formed byrolling in a direction perpendicular to cores of the fusion splicedoptical fibers.

FIG. 13A is a perspective view of an apparatus for applying athermoplastic coating over components of a fiber optic cable assembly,the apparatus including a trough for containing molten thermoplasticmaterial arranged above a heated working surface, with a lateralinsertion slot bounded in part by the working surface in fluidcommunication with the trough cavity and a portion of such a fiber opticcable assembly received in the lateral insertion slot.

FIG. 13B is a side elevation view of one end of the apparatus of FIG.13A

FIG. 14 is a cross-sectional view of an encapsulated optical fiber arrayof a fiber optic cable with non-coplanar groups of fusion splicedoptical fibers that form a 3×4 array.

FIG. 15 is a cross-sectional view of a portion of a fiber optic cablewith non-coplanar groups of fusion spliced optical fibers that form ahexagonal close packed four-layer configuration.

DETAILED DESCRIPTION

Various embodiments will be further clarified by examples in thedescription below. In general, the description relates to a fiber opticcable assembly including at least one spliced (e.g., fusion spliced)optical fiber as well as overlapping bundled sections of strengthmembers that are adhered to one another. A method and an apparatuspermitting fabrication of such a fiber optic cable assembly are furtherprovided.

In this disclosure, the language “strength member,” in the context ofsuch a member arranged within a jacket of a fiber optic cable, refers toa member that extends generally parallel to an optical fiber, istypically flexible in character, and serves to enhance tensile strengthof a fiber optic cable. Typical strength members used in fiber opticcables include aramid yarn (e.g., Kevlar).

Likewise, in this disclosure, the language “bundled section of strengthmembers” or simply “bundled section” refers to a length of strengthmembers that are retained by or otherwise adhered with a bindingmaterial. In certain embodiments, such a binding material may comprise athermoplastic binding material, with one representative exampleincluding polyamide material. In certain embodiments, strength membersmay be generally aligned in a linear array in a bundled section ofstrength members, and therefore resemble a ribbon of strength members.

In this disclosure, the language “fusion spliced optical fiber” refersto two optical fibers that have been fusion spliced together to form apermanent, optical link incorporating the two optical fibers. Thesingular noun “fusion spliced optical fiber” is used even though twooptical fibers are initially present because, after fusion splicing, theresulting optical link is intended to function like a continuous opticalfiber (even though there may be some attenuation resulting from thefusion splice joint). Using the singular form also facilitatesdiscussions involving groups of these fusion spliced optical fibers, aswill be apparent. A fusion spliced optical fiber may desirably include apolymeric overcoating over the fusion splice joint as well as overstripped portions of optical fibers proximate to the fusion splicejoint.

Likewise, in this disclosure, the two optical fibers that define a given“fusion spliced optical fiber” may alternatively be referred to as“optical fiber segments.” Using the language “optical fiber segments”rather than “optical fibers” helps clarify when the disclosure isreferring to one of the pairs of optical fibers that form one of thefusion spliced optical fibers, versus one of the fusion spliced opticalfibers itself.

In certain embodiments, a fiber optic cable assembly includes aplurality of fusion spliced optical fibers in combination with adheredfirst and second bundled sections of strength members, with each splicedoptical fiber including two optical fiber segments that are arrangedserially and joined together by a splice (e.g., a fusion splice) todefine a fusion splice joint. The fusion splice joints of the pluralityof fusion spliced optical fibers define a fusion splice region of thefiber optic cable assembly. The fiber optic cable assembly may include apolymeric overcoating, in which polymeric material beneficiallyovercoats or encapsulates the fusion splice region and stripped sectionsof the optical fibers, and preferably also overcoats portions ofpre-coated sections of the optical fibers proximate to the strippedsections. In certain embodiments, the maximum width and heightdimensions of the polymeric material are only slightly larger thanmaximum width and height dimensions of an array of pre-coated sectionsof the optical fibers proximate to the stripped sections. For example,in certain embodiments, the largest height and width portions of thepolymeric material may correspond to areas in which the polymericmaterial overlaps the pre-coated (i.e., acrylate coated) sections ofoptical fibers. In certain embodiments, the polymeric material overlapregion has a length of at least 1 mm, at least 3 mm, or another lengthspecified herein. If the polymeric material has a thickness in suchregions in a range of from 0.05 to 0.3 mm, then in certain embodiments,the greatest height and/or width portion of the polymeric material mayexceed a greatest height and/or width portion of a corresponding arrayof pre-coated sections of optical fibers (proximate to the strippedsections of optical fibers) by dimensions in one of the followingranges: a range of from 0.1 to 0.6 mm, a range of from 0.2 to 0.6 mm, arange of from 0.1 to 0.5 mm, a range of from 0.2 to 0.5 mm, a range offrom 0.2 to 0.4 mm, a range of from 0.2 to 0.3 mm, a range of from 0.3to 0.6 mm, or a range of from 0.4 mm to 0.6 mm.

Each bundled section of strength members includes a binding material(e.g., a thermoplastic binding material) joining the strength members.In certain embodiments, the binding material used to bind strengthmembers in first and second bundled sections of strength members maycomprise the same polymeric material used to provide a polymericovercoating over fusion splices of the fusion spliced optical fibers. Incertain embodiments, the binding material used to bind strength membersin first and second bundled sections of strength members may comprise apolymeric material that differs from a material used to provide apolymeric overcoating over fusion splices of the fusion spliced opticalfibers.

In one exemplary aspect of the disclosure, a fiber optic cable assemblyincludes an intermediate cable section arranged between first and secondcable sections. The first cable section includes a first jacketcontaining at least one first optical fiber and a plurality of firststrength members, and the second cable section includes a second jacketcontaining at least one second optical fiber and a plurality of secondstrength members. The intermediate cable section includes at least onesplice joint (e.g., fusion splice joint) joining ends of the at leastone first optical fiber and the at least one second optical fiber, andincludes bundled sections of the pluralities of first and secondstrength members, respectively, wherein the first bundled section andsecond bundled section are overlapping and adhered to one another. Anadhesive splice is formed between the adhered bundled sections ofstrength members.

When bundled sections of strength members are adhered to one another, acombined length of the adhered bundled sections is preferably controlledto be shorter than a length of the spliced optical fiber (or fibers) inthe intermediate section of a fiber optic cable assembly to ensure thatthe strength members (instead of the spliced optical fiber(s)) bear anytensile loads that may be applied to the fiber optic cable assemblyfollowing fabrication. This result may be achieved by effectuatingrelative movement between optical fibers on opposing sides of a spliceregion (e.g., by pushing the optical fibers toward one another) to format least one bowed optical fiber region including at least one splicejoint, and then adhering first and second bundled sections of strengthmembers to one another in an overlapping fashion while the at least onebowed optical fiber region is maintained. To achieve such an overlap,relative lengths of optical fibers and strength members emanating fromeach of a first and a second cable section should be adjusted (e.g., bytrimming the optical fibers) to ensure that the one or more opticalfibers are shorter than the strength members of an unjacketed endportion of the cable section before fusion bonding is performed.

In addition to controlling relative lengths of optical fibers andstrength members, an overlap region between bundled sections of strengthmembers adhered to one another has an overlap area that is preferablyselected to meet or exceed a minimum threshold to ensure sufficientcapacity of the splice between bundled sections of strength members tobear an anticipated range of tensile loads that may be applied to afiber optic cable assembly during operation. In certain embodiments, anoverlap area of an overlap region formed by bundled sections of strengthmembers adhered to one another is selected to be at least one of thefollowing thresholds: about 30 mm², about 50 mm², about 70 mm², about 90mm², about 100 mm², about 120 mm², or about 150 mm². It has beenempirically determined that tensile strength of spliced Kevlarstrand-type (i.e., aramid yarn) strength members exceeds 50 pounds offorce when the overlap area is about 90 mm² and when polyamide adhesivematerial is used. If higher strength adhesives are employed betweenbundled sections of strength members, then a smaller overlap areabetween bundled sections may achieve a comparable tensile strengthvalue. In certain embodiments, the above-described overlap area may becalculated as the product of length times width of an overlap betweensubstantially flat first and second bundled sections of strengthmembers.

Direct adhesion between bundled sections of strength members of firstand second cable sections according to fiber optic cable assemblies andfabrication methods disclosed herein avoids the need for mechanicallyattaching strength members to a housing (e.g., by filling a housingcavity with epoxy). In certain embodiments, a tubular covering membermay be provided over an intermediate cable section (i.e., between firstand second cable sections) that includes at least one splice joint aswell as overlapping bundled sections of strength members that areadhered to one another, with the tubular covering member including aninterior volume with at least one unfilled void. Such a tubular coveringmember may surround the intermediate cable section, and also overlapportions of jackets of first and second cable sections, preferably withadhesive material between the tubular covering member and the respectivejackets to secure the tubular covering member and provide a barrierpreventing ingress of dust and/or moisture into the interior volume. Incertain embodiments, an intermediate portion of the tubular coveringmember defines an intermediate interior volume and surrounds theintermediate cable section, with a portion of the intermediate interiorvolume being filled by (i) at least one first and at least one secondoptical fiber with a splice joint therebetween, and desirably includingovercoating material over at least the splice joints, and (ii) first andsecond bundled sections of strength members, wherein another portion ofthe intermediate interior volume embodies at least one unfilled void. Incertain embodiments, an aggregate volume of the at least one unfilledvoid is at least about ten percent (or at least about twenty percent) ofthe intermediate interior volume. This is in contrast to a conventionalepoxy-filled housing, in which even the accidental formation of an airbubble would be unlikely to represent a double-digit percentage of aninterior volume of the housing.

FIG. 7A is a schematic side view illustration of a fiber optic cableassembly 90′ according to one embodiment during a fabrication step priorto addition of a tubular covering member. The fiber optic cable assembly90′ includes first and second cable sections 68A, 68B and anintermediate cable section 91 that contains an overcoated fusion splicedoptical fiber 89 as well as first and second bundled sections ofstrength members 77A, 77B (emanating from the first and second cablesections 68A, 68B, respectively) that are arranged an overlappingconfiguration with an adhesive joint 92 therebetween. The overcoatedfusion spliced optical fiber 89 includes optical fiber segments 70A, 70Bthat are joined by a fusion splice joint 82, with a polymericovercoating material 84 arranged over the fusion splice joint 82 as wellas stripped portions of the optical fiber segments 70A, 70B. Bends 69A,69B provided in the optical fiber segments 70A, 70B form a slight bow inthe overcoated fusion spliced optical fiber 89. As shown, the firstbundled section of strength members 77A has a length 94A that is greaterthan a length of the first optical fiber segment 70A extending between afirst jacket 78A and the splice joint 82, and the second bundled sectionof strength members 77B similarly has a length 94B that is greater thana length of the second optical fiber segment 70B extending between asecond jacket 78B and the splice joint 82. As shown, an overlap distance96 between the first and second bundled sections of strength members77A, 77B may be at least as long as, or longer than, a length of thepolymeric overcoating material 84 in certain embodiments.

FIG. 7B is a schematic side view illustration of a fiber optic cableassembly 90 according to one embodiment substantially identical to thatof FIG. 7A, but with addition of a tubular covering member 98 over theintermediate cable section 91 to cover the overcoated fusion splicedoptical fiber 89 and the first and second bundled sections of strengthmembers 77A, 77B. Ends of the tubular covering member 98 also overlapportions of the jackets 78A, 78B of the first and second cable sections68A, 68B. The tubular covering member 98 defines an interior volume 99that contains the overcoated fusion spliced optical fiber 89 as well asthe adhered, overlapping first and second bundled sections of strengthmembers 77A, 77B. Preferably, the interior volume 99 includes at leastone unfilled void that is devoid of epoxy or other adhesive material,since direct adhesive splicing between the overlapping first and secondbundled sections of strength members 77A, 77B avoids the need for thestrength members to be affixed to the tubular covering member 98.Further, the tubular covering member 98 is preferably devoid of any heatshrink tube arranged over any portions of a splice joint of theovercoated fusion spliced optical fiber 84. The remaining elements ofFIG. 7B are identical to those shown in FIG. 7A and will not bedescribed again.

FIG. 7C is a magnified central portion of FIGS. 7A and 7B including theovercoated fusion spliced optical fiber 89, composed of optical fibersegments 70A, 70B and a solid overcoating 84 of thermoplastic materialhaving a substantially constant outer diameter over the majority of itslength. Each optical fiber segment 70A, 70B includes a coating (e.g., anacrylate coating), with portions of each optical fiber segment 70A, 70Bbeing previously stripped of such coating to form stripped sections 71A,71B embodying glass cladding. Ends of the stripped sections 71A, 71B arefusion spliced at a splice joint 82 to form a fusion spliced opticalfiber. The solid overcoating 84 of polymeric material extends over thesplice joint 82, the previously stripped sections 71A, 71B, and shortlengths 72A, 72B of the coated optical fiber segments 70A, 70B. As shownin FIG. 7C, the solid overcoating 84 may include tapered thickness ends85A, 85B, with a remainder of the solid overcoating 84 having asubstantially constant outer diameter that exceeds an outer diameter ofthe pre-coated optical fiber segments 70A, 70B. The coated optical fibersegments 70A, 70B may each have a nominal outer diameter of 0.25 mm (250μm) in some embodiments. In certain embodiments, the solid overcoating84 of polymeric material may include an outer diameter in a range offrom 0.2 mm to 0.9 mm, from 0.2 mm to 0.7 mm, from 0.2 to 0.5 mm, from0.25 mm to 0.9 mm, from 0.25 to 0.7 mm, or from 0.25 to 0.5 mm.

Although only a single overcoated fusion spliced optical fiber 89 isshown in FIG. 7C, it is to be appreciated that a solid overcoatingsimilar to the solid overcoating 84 shown in FIG. 7C may be applied tomultiple fusion spliced optical fibers arranged in a one-dimensionalarray. In such a situation, the above-described outer diameter valuesfor solid overcoating of polymeric material may correspond to thicknessvalues for the solid overcoating applied to an array of fusion splicedoptical fibers.

In certain embodiments, a polymeric material used to overcoat fusionspliced optical fibers comprises a thermoplastic material that may beheated to a flowable state. In certain embodiments, the polymericmaterial useable to overcoat fusion spliced optical fibers comprises aflowable photopolymerizable adhesive, such as a UV-curable polymericmaterial that may be solidified by impingement of ultraviolet emissionsthereon. In certain embodiments, a polymeric material may be devoid ofUV-curable components. In certain embodiments, a polymeric material in aflowable state comprises a moisture-curable polymeric material or atwo-part adhesive that may be solidified by supplying moisture or acuring agent to the polymeric material. In certain embodiments, fusionspliced optical fibers may be temporarily placed in a cavity (e.g., amold cavity), a housing, a trough, or a container in which polymericmaterial in a flowable state is present, or to which polymeric materialin a flowable state is supplied. In certain embodiments, fusion splicedoptical fibers may be dipped into (or otherwise contacted with) a poolof molten thermoplastic material to effectuate coating. In certainembodiments, a polymeric material that may be used to overcoat portionsof fusion spliced optical fibers may include one or more of polyamide,polyolefin, a polyamide-polyolefin copolymer, a polyamide graftedpolyolefin, and a copolyester. Other polymeric materials (includingthermoplastic materials) may be used. In certain embodiments, apolymeric material that may be used to overcoat portions of fusionspliced optical fibers may include a melt-flow thermoplastic adhesivematerial.

In certain embodiments, a polymeric overcoating as disclosed herein isarranged over a splice joint, as well as over stripped sections andpre-coated sections of fusion spliced optical fibers (e.g., including atleast a short distance of acrylate coated sections proximate to thestripped sections). At least a portion of the polymeric overcoatingincludes a diameter that exceeds a diameter of one or more pre-coatedsections of the fusion spliced optical fibers. Exemplary optical fibersinclude 250 μm or 200 μm diameter acrylate coated fibers without anyadditional buffer layer.

A desirable polymeric overcoating material is preferably not subject todelamination during normal handling over the required service conditionsand lifetime of a fiber optic cable. In certain embodiments, flowablepolymeric material used to fabricate a polymeric overcoating comprisesmolten thermoplastic material. To avoid thermal degradation of one ormore acrylate coating layers of the pre-coated sections of the fusionspliced optical fibers, molten thermoplastic material to be used forovercoating should be maintained at a processing temperature below amelt temperature of the one or more acrylate coating layers. To promoteformation of a suitable overcoating, the molten thermoplastic materialmay also be maintained at a processing temperature at which the moltenthermoplastic material has a melt viscosity in a range of from about 100centipoises (cps) to about 10,000 cps, or more preferably in a subrangeof from about 1,000 cps to about 10,000 cps, or more preferably in asubrange of from about 2,000 cps to about 4,000 cps.

In certain embodiments, desirable thermoplastic overcoating materialsdiffer from conventional melt flow adhesive glue sticks or typicalthermoplastic materials in that they should desirably: have a mediumviscosity (e.g., according to one or more of the ranges outlined above)at a processing temperature, be chemically stable at the processingtemperature, have a glass transition temperature of no greater than −40°C., have a service temperature spanning at least a range of from −40° C.to 85° C. without suffering significant mechanical and/or opticalperformance degradation, exhibit strong adhesion to fiber coating layersand bare glass, be free from charring, and/or exhibit minimal to nooutgassing (e.g., of volatile organic compounds and/or otherconstituents). A glass transition temperature is the point at which amaterial goes from a hard brittle state to a flexible or soft rubberystate as temperature is increased. A common method for determining glasstransition temperature uses the energy release on heating indifferential scanning calorimetry. If a plastic (e.g., thermoplastic)material associated with an optical fiber is exposed to a temperaturebelow its glass transition temperature, then the material will becomevery hard, and the optical fiber may be susceptible to micro bendlosses. In certain embodiments, service temperature of a thermoplasticovercoating material may be determined by compliance with one or moreindustry standards for telecommunication fiber reliability testing, suchas (but not limited to): ITU-T G.652, IED60793-2, Telcordia GR-20-COREand TIA/EIA-492.

Formation of a solid thermoplastic overcoating over at least a shortdistance of pre-coated sections of optical fibers bounding a splicedsegment (e.g., at either end of stripped sections joined at a splicejoint) beneficially ensures that all previously stripped (glass)sections are fully overcoated. In certain embodiments, a solidthermoplastic overcoating extends over a length of a pre-coated sectionof each of the first and second optical fibers, wherein the overcoatedlength of each pre-coated section is in a range of from about 1 mm toabout 10 mm. Additionally, since the solid thermoplastic overcoating mayadhere to one or more coating layers of an optical fiber more readilythan to (pre-stripped) exposed glass sections, providing a solidthermoplastic overcoating of sufficient length to overlap at least ashort distance of pre-coated sections of optical fibers bounding aspliced segment promotes more secure adhesion between the solidthermoplastic overcoating and the fusion spliced segment as a whole. Incertain embodiments, a solid thermoplastic overcoating and a fusionspliced segment utilize a thermoplastic material that is devoid ofadditives configured to promote adhesion to glass, such as silane. Asolid thermoplastic overcoating as disclosed herein is preferably notsubject to delamination during normal handling over the required serviceconditions and lifetime of a fiber optic cable.

In preferred embodiments, a solid thermoplastic overcoating iswater-resistant and serves to block moisture from reaching the splicejoint and the previously stripped glass region of a fusion splicedsegment of optical fibers. This is beneficial since moisture is known tochemically interact with glass cladding of optical fibers and causeexpansion of micro defects in the glass, thereby leading to long-termfailure of optical fibers. The solid thermoplastic overcoating ispreferably also devoid of sharp particles (e.g., inorganic fillerparticles) and air bubbles. The solid thermoplastic overcoating may alsobe devoid of a UV curable material. In certain embodiments, formation ofair bubbles may be reduced by contacting stripped sections andpre-coated sections of fusion spliced first and second optical fiberswith molten thermoplastic material in a subatmospheric pressureenvironment (e.g., in a range of from 0.01 to 0.9, or 0.1 to 0.8, or 0.1to 0.7 times local atmospheric pressure), such as may be attained in apartially evacuated chamber or other enclosure.

Various steps of a method for fabricating a fiber optic cable assemblyincorporating adhered, overlapping bundled sections of strength membersmay be understood with reference to FIGS. 8A-8E.

FIG. 8A is a side view illustration of a fiber optic cable section 101including a jacket 102 containing multiple (e.g., twelve) optical fibers110 and strength members 108 (e.g., of Kevlar aramid yarn) therein, witha length 106 of the optical fibers 110 and strength members 108 beingexposed following removal and peeling back of split portions 104 of thejacket 102. As illustrated, the strength members 108 are dispersed amongthe optical fibers 110.

FIG. 8B is a side view illustration of a fiber optic cable section 100following performance of processing steps relative to the configurationof FIG. 8A—namely, to separate the strength members 108 from the opticalfibers 110, to add a binding material to the strength members 108 toform a bundled section 109 of the strength members 108, and to add abinding material to optical fibers 110 to form a ribbon. In certainembodiments, the strength members 108 may be generally aligned in alinear array in the bundled section 109 to resemble a flat ribbon havinga greater width than height. In certain embodiments, the bindingmaterial may comprise a polymeric binding material as disclosed herein(with such a material potentially being the same as, or different from,any polymeric overcoating material disclosed herein for coating portionsof the optical fibers 110). In certain embodiments, the binding materialmay comprise a thermoplastic binding material, such as (but not limitedto) a polyamide material. In certain embodiments, the binding materialused for bundling strength members is a thermoplastic adhesive materialhaving a softening temperature of at least 120° C., and a shear strengthwhen bonding the strength members 108 of at least 689 kPa (100 psi).

In certain embodiments, strength members 108 may be aligned in agenerally linear array and contacted with polymeric material in aflowable state, and thereafter the polymeric material may be hardened toa solid state to encapsulate or otherwise adhere the strength members108 to form the bundled section 109. As shown in FIG. 8B, the opticalfibers 110 may also be arranged in a linear array to facilitateutilization of a mass fusion splicing process to simultaneously fusionsplice ends of the optical fibers 110 to optical fibers of another fiberoptic cable section (not shown). As further shown in FIG. 8B, followingbundling of the strength members 108 and ribbonization of the opticalfibers 110, end portions 111 of the optical fibers 110 may be removed,such as by cutting the optical fibers 110 along a cut line 113.Following removal of the end portions 111, the remaining optical fibers110 emanating from the jacket (102, shown in FIG. 8A) will be shorter inlength than a length of the bundled sections 109 of strength members 108(with such length corresponding to the length 106 shown in FIG. 8A).

FIG. 8C is a side view illustration of first and second fiber opticcable sections 100A, 100B (each generally in accordance with the fiberoptic cable section 100 shown in FIG. 8B), following the stripping ofacrylate coating material from portions of optical fibers 110A, 110B toform stripped sections 112A, 112B, and following fusion splicing of endsof the stripped sections 112A, 112B at a fusion splice region 114 toform fusion spliced optical fibers 116. In certain embodiments, strippedsections 112A, 112B of each fiber optic cable section 100A, 100B may beat least temporarily ribbonized prior to splicing to maintain consistentspacing for performance of a mass fusion splicing process. The fusionsplicing between ends of stripped sections 112A, 112B is completed priorto adhering the bundled sections 109A, 109B of strength members to oneanother. During such fusion splicing, the bundled sections 109A, 109Bmay be folded in a rearward direction away from the fusion splice region114. The first fiber optic cable section 100A includes multiple firstoptical fibers 110A and multiple first strength members (i.e., embodiedin the first bundled section 109A) exposed following removal and peelingback of split portions 104A of a first jacket 102A. The second fiberoptic cable section 100B includes multiple second optical fibers 110Band multiple second strength members (i.e., embodied in the secondbundled section 109B) exposed following removal and peeling back ofsplit portions 104B of a second jacket 102B. The first and secondbundled sections 109A, 109B of strength members are shown as beingoriented to the same side relative to the fusion spliced optical fibers116.

In certain embodiments, pre-coated (i.e., acrylate coated) opticalfibers subject to being fusion bonded and overcoated (or encapsulated)according to methods disclosed herein are prepared for fusion bonding(e.g., by stripping ends thereof) utilizing non-contact fiber strippingmethods and/or apparatuses, such as those disclosed in U.S. Pat. No.9,167,626 B2 (“the '626 patent”), which is hereby incorporated byreference. Briefly, the '626 patent discloses use of a heater configuredfor heating a heating region to a temperature above a thermaldecomposition temperature of at least one coating of an optical fiber, asecuring mechanism for securely positioning a lengthwise section of theoptical fiber in the heating region, and a controller operativelyassociated with the heater and configured to deactivate the heater nolater than immediately after removal of the at least one coating fromthe optical fiber. Thermal decomposition of at least one coating of anoptical fiber reduces or minimizes formation of flaws in optical fibersthat may be generated by mechanical stripping methods and that canreduce their tensile strength.

FIG. 8D is a side view illustration of an uncovered fiber optic cableassembly 120′ (i.e., lacking a tubular covering member) including thefirst and second fiber optic cable sections 100A, 100B of FIG. 8Cfollowing a step of overcoating the stripped sections 112A, 112B with aovercoating material to form overcoated fusion spliced optical fibers118, and following a step of overlapping and adhering the first andsecond bundled sections 109A, 109B of strength members. During a step ofovercoating the stripped sections 112A, 112B, the bundled sections 109A,109B may be folded in a rearward direction away from the fusion spliceregion 114. The bundled section 109A, 109B form an overlap region 122that may exceed a length of the stripped sections 112A, 112B of theovercoated fusion spliced optical fibers 118. As shown, the first andsecond bundled sections 109A, 109B of strength members are arranged toone side of the overcoated fusion spliced optical fibers 118, and arethus form an overlap region arranged to one side of a plane thatincludes a longitudinal axis definable through cores of the opticalfibers 110A, 110B without the bundled sections 109A, 109B beingdistributed around an entire circumference of a longitudinal axis of anycore of the optical fibers 110A, 110B (e.g., at least in a fusion spliceregion 114, as illustrated in FIG. 8C). As shown in FIG. 8D, theuncovered fiber optic cable assembly 120′ includes an intermediate cablesection 124 arranged between the first and second fiber optic cablesections 100A, 100B. In certain embodiments, the first optical fibers110A may be moved toward the second optical fibers 110B to form at leastone bowed optical fiber region including the fusion splice region 114,and the first and second bundled sections 109A, 109B of strength membersmay be adhered together while the at least one bowed optical fiberregion is maintained. Such steps help ensure that the adhered, bundledsections 109A, 109B of strength members are shorter than the overcoatedfusion spliced optical fibers 118 so that the bundled sections ofstrength members 109A, 109B (instead of the overcoated fusion splicedoptical fibers 118) will bear any tensile loads that may be applied tothe uncovered fiber optic cable assembly 120′ (or applied to a fiberoptic cable assembly including a tubular covering member, such asdescribed in connection with FIG. 8F).

FIG. 8E illustrates the uncovered fiber optic cable assembly 120′ ofFIG. 8D arranged proximate to a metric ruler, showing the intermediatecable section 124 as having a length of 5 cm, and showing theintermediate cable section 124 as having a width comparable to that ofthe first and second jackets 102A, 102B. All elements of FIG. 8E otherthan the metric ruler are identical to those shown in FIG. 8D and willnot be described again.

FIG. 8F is a side view illustration of a fiber optic cable assembly 120substantially similar to the assembly 120′ shown in FIGS. 8D and 8E,following the positioning of a tubular covering member 126 (e.g., a tubeof stainless steel, another metal, plastic, carbon fiber composites, oranother suitable material) to surround the intermediate cable section124 as well as portions of the jackets 102A, 102B of the first andsecond fiber optic cable sections 100A, 100B. An adhesive material (notshown) may be provided between end portions of the tubular coveringmember 126 and the jackets 102A, 102B to promote sealing therebetween,but preferably an interior volume of the tubular covering memberincludes at least one unfilled void (and accordingly is not filledcompletely with epoxy or other potting material). A metric rulerillustrated in the foreground shows a length of the tubular coveringmember 126 as being around 6 cm. Such length is slightly longer than theintermediate cable section 124 to enable the tubular covering member 126to surround portions of the first and second jackets 102A, 102B.

In certain embodiments, the tubular covering member 126 may cover onlythe stripped sections 112A, 112B and splice region 114, and heat shrinktubing may be used to cover the remaining regions between the jackets102A, 102B and the tubular covering member 126.

Consistent with the foregoing discussion of FIGS. 8A-8E, one stepaccording to a method for fabricating a fiber optic cable assemblyincludes processing a first cable section, including at least one firstoptical fiber and a plurality of first strength members within a firstjacket, to bind an unjacketed segment of the plurality of first strengthmembers into a first bundled section of the plurality of first strengthmembers. Another step includes processing a second cable section,including at least one second optical fiber and a plurality of secondstrength members within a second jacket, to bind an unjacketed segmentof the plurality of second strength members into a second bundledsection of the plurality of second strength members. The methodadditionally comprises fusion splicing ends of the at least one firstoptical fiber and the at least one second optical fiber to form at leastone splice joint defining a splice region of the fiber optic cableassembly, wherein each of the at least one first optical fiber and theat least one second optical fiber comprises a stripped portion proximateto the at least one splice joint. The method further comprises forming apolymeric overcoating over the at least one splice joint and over thestripped portion of each of the at least one first optical fiber and theat least one second optical fiber. The method further comprisespositioning the first bundled section of the plurality of first strengthmembers and the second bundled section of the plurality of secondstrength members in an overlapping arrangement, and adhering theoverlapped first and second bundled sections to one another.

In certain embodiments, relative movement is effected between the atleast one first optical fiber and the at least one second optical fiberto form at least one bowed optical fiber region including the at leastone splice joint, and the first and second bundled sections are adheredto one another while the at least one bowed optical fiber region ismaintained. In certain embodiments, any adhesive joining methoddisclosed herein or known in the art may be used to adhere the first andsecond bundled sections. In certain embodiments, the first and secondbundled sections may be adhered to one another using a thermoplasticmaterial.

In certain embodiments, each bundled section of strength members may beformed by contacting a plurality of strength members with at least onepolymeric material in a flowable state and solidifying the at least onepolymeric material to form the section. Thereafter, in certainembodiments, overlapped first and second bundled sections of strengthmembers may be adhered to one another by heating the first and secondbundled sections at or above a melting temperature of the at least onepolymeric material, and re-solidifying the at least one polymericmaterial. In certain embodiments, strength members are generally alignedin a linear array in the first and second bundled sections of strengthmembers.

In certain embodiments, first and second cable sections may each beprocessed to provide unjacketed segments of strength members having alength exceeding a length of unjacketed segments of one or more opticalfibers of the same cable section. This may be accomplished by trimmingoptical fiber segments shorter than strength members following removalof a jacket surrounding the optical fibers and strength members.

In certain embodiments, unjacketed optical fiber segments separated fromstrength members emanating from the same jacket may be initially loose,but subsequently ribbonized to provide consistent spacing between fibersto facilitate utilization of a mass fusion splicing process for formingmultiple splice joints between multiple pairs of optical fibers in asubstantially simultaneous manner. To fabricate an optical fiber ribbon,optical fibers of an unjacketed segment may be contacted with at leastone polymeric material in a flowable state, and the at least onepolymeric material may be solidified. When optical fiber ribbons areused, mass fusion splicing may be performed between ends of opticalfibers of a first optical fiber ribbon and ends of optical fibers of asecond optical fiber ribbon.

Optical fibers of a first plurality of optical fiber segments and of asecond plurality of optical fiber segments to be fusion bonded may bearranged in first and second conventional fiber sorting fixtures,respectively, during stripping and/or fusion bonding steps. A typicalfiber sorting fixture includes a slot having an opening dimension (e.g.,height) that closely matches a corresponding dimension of unbuffered,coated optical fibers to maintain portions of the optical fibersproximate to ends to be stripped (and subsequently fusion spliced) infixed, substantially parallel positions embodying a one-dimensionalarray. In certain embodiments, coated optical fibers having outerdiameters of either 200 μm or 250 μm may laterally abut one another in afiber sorting fixture, such that cores of adjacent optical fibers arealso spaced either 200 μm or 250 μm apart. After stripping of acrylatecoating material from end sections (to form stripped sections) of theoptical fibers, the remaining (bare glass) cladding and core portionsare in a non-contacting (and non-crossing) relationship, and bare glassends of the optical fibers may be fusion bonded using conventionalfusion bonding method steps known to those skilled in the art. Massfusion bonding may be used in any embodiments disclosed herein.Variations of the techniques disclosed in the '626 patent are disclosedin U.S. Pat. Nos. 10,018,782 and 9,604,261, the disclosures of which arealso hereby incorporated by reference herein. Non-contact strippingmethods using lasers or hot gases are also possible in certainembodiments.

FIGS. 9A and 9B illustrate a heating apparatus 132 useable for coatingmultiple fusion spliced optical fibers 116 with thermoplastic material.The multiple fusion spliced optical fibers 116 are composed of a firstgroup of optical fiber segments 110A and a second group of optical fibersegments 110B, with ends of stripped sections 112A, 112B of the opticalfiber segments 110A, 110B being fusion spliced at a fusion splice region114. The heating apparatus 132 includes a body 134 that contains aninternal electric cartridge heater 135. A pool of molten thermoplasticmaterial 130 is arranged atop a substantially level, flat heated surface136. Lateral edges 13A, 13B of the pool of molten thermoplastic material130 extend to lateral edges 138A, 138B of the flat heated surface 136without overflowing, due to lower temperature at the lateral edges 138A,138B as well as surface tension of the molten thermoplastic material130. FIG. 9A illustrates the fusion spliced optical fibers 116 arrangedabove the pool of molten thermoplastic material 130, with the fusionsplice region 114 roughly centered above the pool, and with the lengthof the pool exceeding the combined length of the stripped sections 112A,112B. As shown, the fusion spliced optical fibers 116 are tiltedlaterally (or angled relative to the flat heated surface 136) so that afirst side 126A of the fused optical fibers 116 initially contacts thepool of molten thermoplastic material 130, while a second side 126B ofthe fusion spliced optical fibers 116 remains elevated above the pool.Thereafter, the remainder of the fusion spliced optical fibers 116gradually tilts to a more horizontal orientation and is submerged intothe pool, as shown in FIG. 9B. Such figure shows the stripped sections112A, 112B and the splice region 114 of the fusion spliced opticalfibers 116 submerged in the pool of molten thermoplastic material 130.

Thereafter, the multiple fusion spliced optical fibers 116 may beremoved from the pool of molten thermoplastic material 130 insubstantially a reverse manner from which it was introduced into thepool, and the molten liquid contacting the fusion spliced optical fibers116 may be cooled to yield a solid thermoplastic overcoating thatextends over the previously stripped sections 112A, 112B, the spliceregion 114, and portions of the first and second pluralities of opticalfiber segments 110A, 110B that were previously unstripped. In certainembodiments, the solid thermoplastic overcoating may comprise amelt-flow thermoplastic adhesive material, such as TECHNOMELT® PA 6208polyamide material (Henkel Corp., Dusseldorf, Germany). Such materialexhibits a heat resistance temperature greater than 90° C., a melt flowtemperature lower than 260° C., a melt viscosity between 100 cps and10,000 cps, and a hardness of at least Shore A 45. Further detailsregarding thermoplastic overcoating of fusion spliced optical fibersand/or portions of fiber optic cable assemblies are disclosed inInternational Publication No. WO 2018/175122 published on Sep. 27, 2018,wherein the content of the foregoing publication is hereby incorporatedby reference herein.

Although not specifically shown in FIGS. 9A and 9B, it is to beappreciated that the heating apparatus 132 and pool of moltenthermoplastic material 130 may also be used to form bundled sections ofstrength members, by contacting strength members with the moltenthermoplastic material, then removing the strength members to permit thethermoplastic material to cool and solidify. Another apparatus suitablefor coating multiple fusion spliced optical fibers and for separatelycoating strength members will be described infra, in connection withFIGS. 13A and 13B. Before discussing that apparatus, however, otheritems including bonding of loose fibers with flexible polymer adhesives,and formation of non-coplanar arrangements of fusion spliced opticalfibers, will be introduced.

In certain embodiments, loose optical fibers (which may embodyunjacketed portions of optical fibers emanating from a jacket of a fiberoptic cable) may be bonded by flexible polymer adhesives before beingprocessed by coating, stripping, cleaving, and mass fusion splicing,with such bonding being useful to provide dimensional stability of thefibers during subsequent processing steps such as polymeric materialovercoating/encapsulation as well as positioning of optical fiber groupsinto a configuration other than a one-dimensional array. In such anembodiment, at least portions of flexible polymer adhesive material maybe overcoated with polymeric material during one or more steps ofpolymeric material overcoating or encapsulation. In one embodimentinvolving a first group of loose, pre-coated (i.e., acrylate coated)optical fibers, the first group of optical fibers may be flexiblyadhered into a first one-dimensional flexible fiber array having alength of at least about 60 mm. Thereafter, coating material may bestripped from ends of the first group of pre-coated optical fibers, andstripped ends of the first group of pre-coated optical fibers may becleaved to form stripped sections of optical fibers suitable for fusionsplicing. If the first group of optical fibers is to be fusion splicedto a second group of loose, pre-coated optical fibers, then the secondgroup of optical fibers may be flexibly adhered into a secondone-dimensional flexible fiber array having a length of at least about60 mm. Thereafter, coating material may be stripped from ends of thesecond group of pre-coated optical fibers, and stripped ends of thesecond group of pre-coated optical fibers may be cleaved to formstripped sections of optical fibers also suitable for fusion splicing.

FIG. 10A is a perspective view of a portion of a fiber optic cablesubassembly 139 during fabrication, with twelve fusion spliced opticalfibers 142 arranged in a one-dimensional array, and being devoid ofovercoating material over stripped portions 146A, 146B of the fusionspliced optical fibers 142. The fusion spliced optical fibers 142include first and second pluralities of fiber optic segments 142A, 142Bthat each include a pre-coated section 149A, 149B and a stripped portion146A, 146B, with ends of the stripped portions 146A, 146B being fusionspliced to one another at the fusion splice region 148. As shown,flexible polymer adhesive binding material regions 143A, 143B areprovided over portions of the pre-coated sections 149A, 149B of thefirst and second pluralities of fiber optic segments 142A, 142B. Incertain embodiments, flexible polymer adhesive binding material 143A,143B may be used to flexibly adhere fiber optic segments of the firstand second pluralities of fiber optic segments 142A, 142B prior tostripping of acrylate coating material from ends of the fiber opticsegments 142A, 142B, and prior to cleaving of stripped ends of fiberoptic segments 142A, 142B. At least portions of flexible polymeradhesive binding material regions 143A, 143B are subject to beingsubsequently overcoated with polymeric material during overcoating ofthe stripped portions 146A, 146B and the fusion splice region 148.

FIG. 10B illustrates an optical fiber portion of a fiber optic cableassembly 140 incorporating the subassembly of FIG. 10A, followingformation of a polymeric overcoating 144 extending over the strippedportions 146A, 146B and the fusion splice region 148. The polymericovercoating 144 further extends over portions of the flexible polymeradhesive binding material regions 143A, 143B to form polymeric materialoverlap regions 145A, 145B. In certain embodiments, a length of eachpolymeric material overlap region 145A, 145B is at least about 3 mm in adirection parallel to fiber cores of the fusion spliced optical fibers142. The remaining elements of FIG. 10B are identical to those describedin FIG. 10A, and will not be described again for sake of brevity. It isto be appreciated that FIGS. 10A and 10B illustrate only optical fiberportions of a fiber optic cable assembly, without showing bundledsections of strength members and jackets as included in embodimentsdescribed herein.

In certain embodiments, a plurality of fusion spliced optical fibershave a non-coplanar arrangement at the fusion splice region of a fiberoptic cable assembly, to provide a reduced aggregate width of theplurality of fusion spliced optical fibers. A “non-coplanar arrangement”in the fusion splice region is an arrangement in which the opticalfibers of a plurality of fusion spliced optical fibers are notexclusively aligned (or exclusively substantially aligned) in a commonplane that extends in a lengthwise direction of the fiber optic cable.In other words, there is no common plane, extending in a lengthwisedirection of the fiber optic cable, that intersects all fusion splicedoptical fibers at the fusion splice region (i.e., no substantialalignment in a common plane); or more specifically, there is no commonplane, extending in a lengthwise direction of the fiber optic cable,that intersects a fiber core or each of the fusion spliced opticalfibers at the fusion spliced region (i.e., no alignment in a commonplane). Thus, “substantial alignment” refers to the fusion splicedoptical fibers in general, whereas “alignment” is more precise andrefers to fiber cores of the fusion spliced optical fibers. As can beappreciated, due to the non-coplanar arrangement at the fusion spliceregion, the fusion spliced optical fibers are not exclusively arrangedin a one-dimensional array in a cross-sectional view perpendicular tothe lengthwise direction of the fiber optic cable. Such an arrangementdoes not preclude the presence of two or more groups of fusion splicedoptical fibers arranged in different one-dimensional arrays that incombination form a multi-dimensional array, so long as all fusionspliced optical fibers of the plurality of fusion spliced optical fibersare not arranged in a single one-dimensional array. The non-coplanararrangement of fusion spliced optical fibers can be expressed byconsidering there to be multiple groups of the fusion spliced opticalfibers, still with a polymeric overcoating extending over a fusionsplice region as well as over a stripped section of each optical fibersegment. To this end, in certain embodiments, a first group of fusionspliced optical fibers is arranged non-coplanar to a second group of thefusion spliced optical fibers at the fusion splice region.

As noted previously, current mass fusion splice technology and currentfusion splice protection technology only support one-dimensional arraysof optical fiber splices. Fiber optic cable assemblies according tocertain embodiments disclosed herein may include mass fusion splicedoptical fibers that are repositioned (after fusion splicing iscompleted) to a configuration other than a one-dimensional array, andovercoated or encapsulated with polymeric material.

In certain embodiments, during fabrication of a fiber optic cableassembly, mass fusion spliced first and second pluralities of opticalfiber segments may be initially arranged in a one-dimensional array toform a plurality of fusion spliced optical fibers. Thereafter, strippedsections of the fusion spliced optical fibers may be contacted withpolymeric material in a flowable state. Either before or after thecontacting of stripped sections with flowable (e.g., molten) polymericmaterial, the position of at least some of the fusion spliced opticalfibers may be rearranged to yield a configuration in which the fusionspliced optical fibers have a non-coplanar arrangement at the fusionsplice region. Thereafter, the polymeric material may be solidified withthe fusion spliced optical fibers in the non-coplanar arrangement at thefusion splice region.

In certain embodiments, solidified polymeric material forms a polymericovercoating that encapsulates the fusion splice region and the strippedsections of each optical fiber segment of the plurality of fusionspliced optical fibers. Such overcoating may also extend over a portionof a pre-coated (unstripped) section of each optical fiber.

The altering of position of at least some of the fusion spliced opticalfibers to yield a configuration in which the plurality of fusion splicedoptical fibers have a non-coplanar arrangement at the fusion spliceregion may be performed either before or after the fusion splicedoptical fibers are contacted with polymeric material in a flowablestate. In certain embodiments, the contacting of the fusion splices aswell as at least a portion of the stripped sections of the fusionspliced optical fibers with a polymeric material in a flowable state isperformed prior to the altering of position of at least some fusionspliced optical fibers. Conversely, in certain embodiments, thecontacting of the fusion splices as well as at least a portion of thestripped sections of the fusion spliced optical fibers with a polymericmaterial in a flowable state is performed after the altering of positionof at least some fusion spliced optical fibers. In certain embodiments,the contacting of at least a portion of the stripped sections withpolymeric material in a flowable state comprises (i) coating at least aportion of the stripped sections with a first portion of polymericmaterial prior to the altering of position of at least some fusionspliced optical fibers; and (ii) coating at least a portion of thestripped sections with a second portion of polymeric material prior tothe altering of position of at least some fusion spliced optical fibers.In certain embodiments, the first portion of polymeric material may becompositionally the same as the second portion of polymeric material, orthe first and second portions of polymeric material may becompositionally different.

Various methods may be used to solidify polymeric material in a flowablestate, depending on the character of the polymeric material. In certainembodiments, polymeric material may be solidified by supplying achemical (e.g., a polymerization agent, which may optionally includewater) to promote cross-linking between polymer chains. In certainembodiments, solidifying of the polymeric material may be accomplishedby cooling the polymeric material. In certain embodiments, thecontacting of at least a portion of the stripped section of each opticalfiber segment of the plurality of fusion spliced optical fibers with thepolymeric material in a flowable state is performed prior to thealtering of position of at least some fusion spliced optical fibers, andthe altering of position of at least some fusion spliced optical fibersis performed while the polymeric material in a flowable state ismaintained at a melt flow temperature of the polymeric material.

In certain embodiments, polymeric material may be in a flowable statewhen initially contacted with stripped sections of optical fibersegments and fusion splices, at least partially solidified, andsubsequently reflowed and resolidified. In certain embodiments, thecontacting of at least a portion of the stripped sections of eachoptical fiber segment of the plurality of fusion spliced optical fiberswith the polymeric material in a flowable state comprises coating thestripped sections with the polymeric material in a flowable state, andthe contacting is performed prior to the altering of position of atleast some fusion spliced optical fibers of the plurality of fusionspliced optical fibers. Thereafter, the altering of position of at leastsome fusion spliced optical fibers of the plurality of fusion splicedoptical fibers comprises stacking a first group of fusion splicedoptical fibers of the plurality of fusion spliced optical fibers over asecond group of fusion spliced optical fibers of the plurality of fusionspliced optical fibers with polymeric material (coated on the strippedsections during the contacting step) arranged therebetween. In such acase, the polymeric material may be reheated after the altering ofposition of at least some fusion spliced optical fibers of the pluralityof fusion spliced optical fibers to reflow and merge polymeric materialarranged between (i) the first group of fusion spliced optical fibersand (ii) the second group of fusion spliced optical fibers.

In certain embodiments, the contacting at least a portion of thestripped sections of the fusion spliced optical fibers with polymericmaterial in a flowable state may include coating at least a portion ofthe stripped sections with a first portion of polymeric material priorto the altering of position of at least some spliced optical fibers ofthe plurality of fusion spliced optical fibers, and coating at least aportion of the stripped sections with a second portion of polymericmaterial in a flowable state after the altering of position of at leastsome spliced optical fibers of the plurality of fusion spliced opticalfibers. Restated, such a method may include an initial polymericmaterial contacting step, followed by positioning of groups of fusionspliced optical fibers into a configuration other than a one-dimensionalarray, followed by a subsequent polymeric material contacting step.

Any reference herein to non-coplanar first and second groups of fusionspliced optical fibers is neither intended to limit, nor serves tolimit, the subject matter disclosed herein to fusion spliced opticalfibers with fiber cores disposed in first and second planes such as a“two row” array. Any suitable configuration for arranging multiplegroups of fusion spliced optical fibers, other than exclusively in aone-dimensional array, is contemplated by such language. In certainembodiments, a third group of fusion spliced optical fibers may befurther provided, wherein at the fusion splice region, a third plane isdefinable through substantially parallel fiber cores of at least twooptical fibers of the third group of fusion spliced optical fibers, withthe first, second, and third planes being non-coplanar. In certainembodiments involving a total of twelve fusion spliced optical fibers,the fusion splice region may be configured as a 2×6 array, a 3×4 array,or a hexagonal close packed four-layer configuration, respectively. Incertain embodiments, fusion spliced optical fibers may be placed in aspiral configuration so long as the fusion spliced optical fibers remainsubstantially parallel to one another (e.g., within one degree or withintwo degrees of deviation from parallel at any one position). Otherconfigurations may be provided for groups of twelve fusion splicedfibers or for groups of fusion spliced fibers other than twelve innumber. In certain embodiments, each group of optical fiber segments tobe spliced may include 8, 12, 16, or 24 optical fibers. Other numbers ofoptical fibers may be provided. In certain embodiments, non-coplanarfirst and second groups of fusion spliced optical fibers each include atleast three, or at least four, fusion spliced optical fibers. Suchoptical fibers may include single mode optical fibers or multi-modeoptical fibers.

Various methods may be used to alter position of at least some fusionspliced optical fibers. In certain embodiments, mass fusion splicedfibers may be overcoated with thermoplastic material and separated intoa number of subarrays each including multiple coated optical fibers. Thesubarrays are then stacked in a fixture, and polymer coated spliceregions are heated above the melt flow temperature of the thermoplasticmaterial and subsequently cooled. Such process causes the thermoplasticovercoating between the subarrays to coalesce and form an encapsulatedtwo-dimensional high density encapsulated splice.

In certain embodiments, the altering of position of at least somespliced optical fibers of a plurality of fusion spliced optical fibersincludes rolling the at least some spliced optical fibers in a directionperpendicular to fiber cores of the spliced optical fibers. Such a stepmay be useful for forming an overcoated fiber optic cable portion havinga cross-section in a hexagonal close-packed configuration. In certainembodiments, such rolling may be combined with twisting to form anovercoated fiber optic cable portion having optical fibers arranged in aspiral configuration.

In certain embodiments, the altering of position of at least somespliced optical fibers of a plurality of fusion spliced optical fibersincludes folding of a first group fusion spliced optical fibers (e.g.,in a direction perpendicular to fiber cores of fusion spliced opticalfibers) in a manner causing the first group of fusion spliced opticalfibers to overlie the second group of fusion spliced optical fibers.Such a step may be useful for forming an overcoated fiber optic cableportion having a cross-section with a rectangular shape. As analternative to folding, in certain embodiments the altering of positionof at least some spliced optical fibers of a plurality of fusion splicedoptical fibers may include stacking a first group of fusion splicedoptical fibers over a second group of fusion spliced optical fibers.

FIGS. 11A and 11B provide perspective and cross-sectional views,respectively, of a fiber optic cable 150 with twelve fusion splicedoptical fibers 152 arranged in a 2×6 array, and overcoating material 154that extends over stripped sections 156A, 156B of the fusion splicedoptical fibers 152 and over a fusion splice region 158. The fusionspliced optical fibers 152 include first and second pluralities of fiberoptic segments 152A, 152B that each include a pre-coated section 160A,160B and a stripped section 156A, 156B, with ends of the strippedsections 156A, 156B being fusion spliced to one another at the fusionsplice region 158. The overcoating material 154 has a length Lsufficient to cover not only the stripped sections 156A, 156B and thefusion splice region 158, but also portions of the pre-coated sections160A, 160B of the fusion spliced optical fibers 152 to form overlapregions 162A, 162B. FIG. 11B provides a cross-sectional view takenthrough one of these overlap regions 162A. Referring to FIG. 11B, in theoverlap region 162A, each fusion spliced optical fiber 152 includes aglass core, glass cladding 166, and an acrylate coating 168. As shown,the acrylate coating 168 of each optical fiber 152 may be arranged incontact with an acrylate coating of at least one other optical fiberwithin the 2×6 array; however, in the stripped sections 156A, 156B ofFIG. 11A, the stripped (glass) sections 156A, 156B are arranged inparallel without contacting one another, and the overcoating material154 directly contacts glass material (i.e., cladding material 166 asshown in FIG. 9B) of the stripped sections 156A, 156B. With continuedreference to FIG. 11B, the array of optical fibers 152 may be segregatedin two optical fiber groups 165-1, 165-2. Within each optical fibergroup 165-1, 165-2, a plane P₁, P₂, is definable through glass cores ofat least two (or as illustrated, six) optical fibers of that group. Asshown, the two planes P₁, P₂ are non-coplanar. The 2×6 arrayconfiguration of fusion spliced optical fibers 152 shown in FIGS. 11Aand 11B is significantly narrower than a width that would result fromarranging the twelve fusion spliced optical fibers 152 in a 1×12 array(although not as narrow as a 3×4 array configuration to be discussed inconnection with FIG. 14 ). The fusion spliced optical fibers 152 shownin FIGS. 11A and 11B is amenable to being positioned in the depicted 2×6array configuration by two-layer folding, which is simpler than forminga three-layer array (e.g., 3×4 array) or four-layer array (e.g.,hexagonal packed array) as disclosed herein. In certain embodiments, themaximum cross-sectional dimension of an encapsulated area of the fiberoptic cable 150 (e.g., corresponding to one of the overlap regions 162A,162B) is 1.67 mm, which enables the fiber optic cable 150 to fit into a3 mm outer diameter cable jacket.

FIG. 12 is a perspective view of a portion of a fiber optic cablesubassembly 170 during fabrication, showing an overcoated second groupof fusion spliced optical fibers 177B in a state of being folded, withthe intention of subsequently being positioned to overlap an overcoatedfirst group of fusion spliced optical fibers 177A. The fusion splicedoptical fibers encompass first and second pluralities of fiber opticsegments 182A, 18B that each include a pre-coated section 180A, 180B anda stripped section 176A, 176B, with ends of the stripped sections 176A,176B being fusion spliced to one another at the fusion splice region178. Overcoating material 174 extends over the stripped sections 176A,176B, over the fusion splice region 178, and over portions of thepre-coated sections 180A, 180B to form overlap regions 182A, 182B. Asshown, a second group of overcoated fusion spliced optical fibers 177Bis vertically oriented and extends higher than a first group ofhorizontally arranged overcoated fusion spliced optical fibers 177A.With continued folding of the second group of overcoated fusion splicedoptical fibers 177B by application of the folding force F, the secondgroup of overcoated fusion spliced optical fibers 177B may be stackedatop the first group of overcoated fusion spliced optical fibers 177A.If the overcoating material 174 embodies thermoplastic material, then incertain embodiments, reheating of the overcoating material 174 may causereflow of the overcoating material 174 between the first and secondgroups of overcoated fusion spliced optical fibers 177A, 177B sufficientto adhere these groups together after cooling of the overcoatingmaterial 174.

FIGS. 13A and 13B illustrate of an apparatus 190 useful for: (i)applying a thermoplastic coating over components of a fiber optic cableassembly (such as over fusion spliced optical fibers and over groups ofstrength members to form bundled sections of strength members), (ii)altering position of fusion spliced optical fibers to yield non-coplanararrangement at the fusion splice region, and (iii) promoting adhesionbetween overlapping bundled sections of strength members.

The apparatus 190 includes a support member 192 defining a workingsurface 194 with first and second longitudinal recesses 196, 198 definedin the support member 192 and each having a floor 196A, 196B that isrecessed relative to the working surface 194. The support member 192 isbounded laterally by left and right side surfaces 192A, 192B and a frontsurface 193, wherein the longitudinal recesses 196, 198 extend over anentire width of the support member 192 to penetrate the left and rightside surfaces 192A, 192B. As shown, the first and second longitudinalrecesses 196, 198 each have a constant width in a directionperpendicular to the front surface 193, but a width and depth dimensionsof the first and second longitudinal recesses 196, 198 differ from oneanother. A front working surface portion 194A may be arranged lower thana remainder of the working surface 194.

The apparatus 190 further includes a trough 200 arranged above theworking surface 194 and defining a trough cavity 202 configured toretain a pool of molten thermoplastic material. The trough 200 isbounded by a rear wall 204, a front wall 206, side walls 208, 210, and aportion of the working surface 194. A lateral insertion slot 212 extendsbetween the working surface 194 and the front wall 206 of the trough200, and further extends between the working surface 194 and at leastportions of the side walls 208, 210, with the lateral insertion slot 212not extending through the rear wall 204. The lateral insertion slot 212is provided in fluid communication with the trough cavity 202. Despitethe presence of the lateral insertion slot 212 providing an opening tothe trough cavity 202, molten thermoplastic material may remainsubstantially within the trough cavity 202 without escaping through thelateral insertion slot 212 due to lower temperature at external portionsof the lateral insertion slot 212 in contact with ambient air, incombination with surface tension of the molten thermoplastic material.In certain embodiments, the lateral insertion slot 212 includes a heightof about 0.33 mm.

Opposing pairs of vertical slots 214, 216 extend downward from an uppersurface 211 of the side walls 208, 210 of the trough 200. A bodystructure 218 arranged below the support member 192 contains a heatingelement 220, which may embody a resistive heating element such as aresistive cartridge heater, and may include an associated temperaturesensor (e.g., thermocouple, thermistor, or the like) to permittemperature to be controlled. As shown, the body structure 218 may havelateral dimensions smaller than the support member 192. The bodystructure 218 is configured to transfer heat from the heating element220 to the support member 192 and the working surface 194 by thermalconduction. As shown in FIG. 13A, a fiber optic cable assembly portion222 (e.g., including multiple optical fibers arranged in a linear arraysuch as a ribbon) is received by the lateral insertion slot 212.

During use of the apparatus 190, spliced optical fibers (such asembodied in the fiber optic cable assembly portion 222) may be slidlaterally into the lateral insertion slot 212 to be coated by moltenthermoplastic material, and after sliding out, the thickness of thethermoplastic material coating is set by the thickness (i.e., height) ofthe lateral insertion slot 212. To ribbonize loose optical fibers, theoptical fibers may first be sorted into a one-dimensional array and thenslid laterally into the lateral insertion slot 212. The optical fibersmay then be pulled longitudinally through the bath of moltenthermoplastic material, wherein a thickness of a resulting fiber ribbonis again determined by the thickness of the lateral insertion slot 212.The same apparatus 190 may be used for binding strength members intobundled sections. In one embodiment, strength members such as Kevlararamid yarn fibers are first held by a clip with a predetermined width.The strength members are then slid laterally into the lateral insertionslot 212 to contact molten thermoplastic material retained in the troughcavity 202. The strength members soaked with molten thermoplasticmaterial can be slid out of the trough cavity in either a longitudinalor lateral direction, wherein after cooling a bundled section ofstrength members is formed. The thickness of the resulting bundledsection of strength members is again set by the thickness of the lateralinsertion slot 212.

Other features of the apparatus 190 are beneficial for producing fiberoptic cable assemblies as disclosed herein. In certain embodiments, thelongitudinal recesses 196, 198 defined in the support member 192 may beused to promote formation of encapsulated optical fiber arrays havingnon-coplanar groups of fusion splice optical fibers. Following removalof a thermoplastically coated one-dimensional array of fusion splicedoptical fibers from the lateral insertion slot 212, such an array may bepositioned over one of the longitudinal recesses 196, 198 of desiredsize and folded (or rolled) therein to reposition at least some of thefusion spliced optical fibers in a two-dimensional array. Additionally,the working surface 194 may be used to effectuate heating and reflow ofbinding material of overlapping bundled sections of strength members toadhere the bundled sections to one another.

In certain embodiments, the apparatus 190 may be fabricated of one ormore suitably thermally conductive materials such as aluminum, stainlesssteel, or the like. In certain embodiments, one or more surfaces (orsurface portions) of the apparatus may be anodized and/or coated with anon-stick material.

FIG. 14 is a cross-sectional view of an encapsulated optical fiber array230 of a fiber optic cable showing twelve fusion spliced optical fibers232 arranged in a 3×4 array, and overcoating material 234 that extendsover the fusion spliced optical fibers 232. Unstripped portions of thefusion spliced optical fibers 232 (e.g., distal from a fusion spliceregion) are shown, with each fusion spliced optical fiber 232 includinga glass core 244, glass cladding 246, and an acrylate coating 248. Asillustrated, the acrylate coating 248 of each optical fiber 232 may bearranged in contact with an acrylate coating 248 of at least one otheroptical fiber 232 within the 3×4 array in unstripped optical fiberregions of the encapsulated optical fiber array 230. It is to beappreciated that in stripped portions of optical fibers (not shown) ofthe encapsulated optical fiber array 230, the overcoating material 234may directly contact glass cladding 246 of the fusion spliced opticalfibers 232. With continued reference to FIG. 14 , the array of fusionspliced optical fibers 232 may be segregated in three optical fibergroups 245-1, 245-2, 245-3. Within each optical fiber group 245-1,245-2, 245-3, a plane P₁, P₂, P₃ is definable through glass cores 244 ofat least two (or as illustrated, three) optical fibers of that group. Asshown, the three planes P₁, P₂, P₃ are non-coplanar. The 3×4 arrayconfiguration of fusion spliced optical fibers 232 shown in FIG. 14 issignificantly narrower than a width that would result from arranging thetwelve fusion spliced optical fibers 232 in a one dimensional (i.e.,1×12) array. In certain embodiments, the maximum cross-sectionaldimension (e.g., maximum width) of an encapsulated area of the opticalfiber array 230 is within a diameter of 1.3 mm, which enables theoptical fiber array 230 of the fiber optic cable to easily fit into the1.5 mm inner diameter of a 2 mm outer diameter cable jacket. Thisdimension is significantly reduced in comparison to the 3.1 mm width ofa standard optical fiber ribbon containing twelve optical fibers.

FIG. 15 is a cross-sectional view of an encapsulated optical fiber array250 of a fiber optic cable with twelve fusion spliced optical fibers 252arranged in a hexagonal close packed four-layer configuration, andovercoating material 254 that extends over the fusion spliced opticalfibers 252. Unstripped portions of the fusion spliced optical fibers 232(e.g., distal from a fusion splice region) are shown, with each fusionspliced optical fibers 252 including a glass core 264, glass cladding266, and an acrylate coating 268. As shown, the acrylate coating 268 ofeach optical fiber 252 may be arranged in contact with an acrylatecoating 268 of at least one other optical fiber 252 within the hexagonalclose packed four-layer configuration in unstripped optical fiberregions of the encapsulated optical fiber array 250, whereas incross-sections of the encapsulated optical fiber array corresponding tostripped portions of optical fibers (not shown), the overcoatingmaterial 254 may directly contact the glass cladding 268 of the fusionspliced optical fibers 252. With continued reference to FIG. 15 , thehexagonal close packed four-layer configuration of optical fibers 252may be segregated in four optical fiber groups 265-1, 265-2, 265-3,265-4. Within each optical fiber group 265-1, 265-2, 265-3, 265-4, aplane P₁, P₂, P₃, P₄ is definable through glass cores 264 of at leasttwo (or as illustrated, three or four in certain instances) opticalfibers of that group. As shown, the four planes P₁, P₂, P₃, P₄ arenon-coplanar. The hexagonal close packed four-layer configuration offusion spliced optical fibers 252 shown in FIG. 15 is significantlynarrower than a width that would result from arranging the twelve fusionspliced optical fibers 252 in a 1×12 array, and also narrower than the2×6 and 3×4 array configurations shown in FIG. 11B and FIG. 14 ,respectively. In certain embodiments, the maximum cross-sectionaldimension of an encapsulated area of the encapsulated fiber array 250 is1.0 mm, which enables the encapsulated optical fiber array 150 to fitinto a 3 mm outer diameter cable jacket.

It is to be appreciated that the encapsulated optical fiber arrays 230,250 of FIGS. 14 and 15 , respectively, may be incorporated into a fiberoptical cable assembly including a jacket as well as overlapping,adhered bundled sections of strength members as disclosed previouslyherein.

EXAMPLE

An example demonstrating the fabrication of a fiber optic cable assemblyincorporating fusion splices between two twelve-fiber trunk cables willnow be described in connection with FIGS. 8A-8F. With reference to FIG.8A, starting with a 3.0 mm outer diameter jacketed pigtail cable section101 containing Kevlar strength members 108 and twelve optical fibers110, a section of the cable jacket about 70 mm in length is removed orslit open to expose the optical fibers 110 and the Kevlar strengthmembers 108. Following separation of the strength members 108 from theoptical fibers 110, the apparatus 190 of FIGS. 13A and 13B is used (i)to ribbonize the unjacketed optical fibers 110 by inserting themlaterally into the lateral insertion slot 212 to contact moltenthermoplastic material, and (ii) to form a bundled section 109 ofstrength members 108 by inserting the strength members 108 laterallyinto the lateral insertion slot 212 to contact molten thermoplasticmaterial. The apparatus 190 is used to form a bundled section 109 ofKevlar strength members 108 having dimensions of 30 mm long, 3 mm wide,and 0.33 mm thick. FIG. 8B shows a fiber optic cable section 100including resulting bundled section 109 of strength members 108 and theribbonized optical fibers 110. The foregoing process is performed twiceto form identical first and second cable fiber optic sections 100A, 100B(shown in FIG. 8C), each in accordance with the fiber optic cablesection 100 of FIG. 8B.

Starting with the first and second fiber optic cable sections 100A,100B, end portions of the ribbonized optical fibers 110A, 110B arestripped, cleaved, fusion spliced at splice region 114, and then coatedwith a thin layer of hot melt adhesive as matrix protection material.The bundled sections 109A, 109B of Kevlar strength members are trimmedand oriented to the same side of the fiber splice. The result is shownin FIG. 8C.

Thereafter, the bundled sections 109A, 109B of Kevlar strength membersare clamped in a stacked configuration (one on top of the other) whilekeeping the aggregate length of the stacked bundled sections 109A, 109Bbundled slightly shorter than the fusion spliced optical fibers 116. Theoverlapped bundled sections 109A, 109B of Kevlar strength members areheated to about 200° C. to re-melt the hot melt adhesive previouslyapplied to bind strength members of each bundled section 109A, 109B.After cooling in a few seconds, the bundled sections 109A, 109B ofKevlar strength members are bonded together. Because the protectivecoating of the ribbon fiber splice is thin, the fusion spliced opticalfibers 116 and the overlapping bundled sections 109A, 109B of strengthmembers are virtually parallel. The resulting uncovered fiber opticcable assembly 120′ is shown in FIGS. 8D and 8E. Thereafter, a tubularcovering member 126 embodied in a stainless steel tube may be slidlaterally to cover the fusion spliced optical fibers 116 and theoverlapping bundled sections 109A, 109B of strength members, and tooverlap the jackets 102A, 102B of the first and second fiber optic cablesections 100. Short lengths of the split portions 104A, 104B (shown inFIGS. 8A-8D) of the jackets 102A, 102B are retained within the tubularcovering member 126 to provide additional bonding surface area. Fastcuring adhesive is applied to bond ends of the jackets 102A, 102B to theends of the tubular covering member 126. The tubular covering member 126completely encloses an intermediate cable section 124 including thefusion spliced optical fibers 116 as well as the overlapping and adheredbundled sections 109A, 109B of strength members.

Those skilled in the art will appreciate that various modifications andvariations can be made without departing from the spirit or scope of theinvention. Since modifications, combinations, sub-combinations, andvariations of the disclosed embodiments incorporating the spirit andsubstance of the invention may occur to persons skilled in the art, theinvention should be construed to include everything within the scope ofthe appended claims and their equivalents. The claims as set forth beloware incorporated into and constitute part of this detailed description.

It will also be apparent to those skilled in the art that unlessotherwise expressly stated, it is in no way intended that any method inthis disclosure be construed as requiring that its steps be performed ina specific order. Accordingly, where a method claim below does notactually recite an order to be followed by its steps or it is nototherwise specifically stated in the claims or descriptions that thesteps are to be limited to a specific order, it is no way intended thatany particular order be inferred.

What is claimed is:
 1. A method for fabricating a fiber optic cableassembly, the method comprising: processing a first cable section,including at least one first optical fiber and a plurality of firststrength members within a first jacket, to bind an unjacketed segment ofthe plurality of first strength members into a first bundled section ofthe plurality of first strength members; processing a second cablesection, including at least one second optical fiber and a plurality ofsecond strength members within a second jacket, to bind an unjacketedsegment of the plurality of second strength members into a secondbundled section of the plurality of second strength members; fusionsplicing ends of the at least one first optical fiber and the at leastone second optical fiber to form at least one splice joint defining asplice region of the fiber optic cable assembly, wherein each of the atleast one first optical fiber and the at least one second optical fibercomprises a stripped portion proximate to the at least one splice joint;forming a polymeric overcoating over the at least one splice joint andover the stripped portion of each of the at least one first opticalfiber and the at least one second optical fiber; and positioning thefirst bundled section of the plurality of first strength members and thesecond bundled section of the plurality of second strength members in anoverlapping arrangement, and adhering the overlapped first and secondbundled sections to one another; wherein the fiber optic cable assemblyis devoid of a heat shrink tube arranged over the at least one splicejoint.
 2. The method of claim 1, further comprising effecting relativemovement between the at least one first optical fiber and the at leastone second optical fiber to form at least one bowed optical fiber regionincluding the at least one splice joint, and adhering the first andsecond bundled sections to one another while the at least one bowedoptical fiber region is maintained.
 3. The method according to claim 1,wherein: the binding of the unjacketed segment of the plurality of firststrength members comprises contacting the plurality of first strengthmembers with at least one polymeric material in a flowable state andsolidifying the at least one polymeric material to form the firstbundled section; the binding of the unjacketed segment of the pluralityof second strength members comprises contacting the plurality of secondstrength members with the at least one polymeric material in a flowablestate and solidifying the at least one polymeric material to form thesecond bundled section; and the adhering of the overlapped first andsecond bundled sections to one another comprises heating the first andsecond bundled sections at or above a melting temperature of the atleast one polymeric material, and re-solidifying the at least onepolymeric material.
 4. The method according to claim 1, wherein: theprocessing of the first cable section comprises providing the unjacketedsegment of the plurality of first strength members having a lengthexceeding a length of an unjacketed segment of the at least one firstoptical fiber extending beyond the first jacket toward the spliceregion; and the processing of the second cable section comprisesproviding the unjacketed segment of the plurality of second strengthmembers having a length exceeding a length of an unjacketed segment ofthe at least one second optical fiber extending beyond the second jackettoward the splice region.
 5. The method according to claim 1, whereinthe first strength members of the plurality of first strength membersare generally aligned in a linear array in the first bundled section,and the second strength members of the plurality of second strengthmembers are generally aligned in a linear array in the second bundledsection.
 6. The method according to claim 1, wherein: a longitudinalaxis is definable in a direction generally parallel to a core of the atleast one first optical fiber and a core of the at least one secondoptical fiber at the splice region; and the first and second bundledsections are arranged to one side of the longitudinal axis without beingdistributed around an entire circumference of the longitudinal axis. 7.The method according to claim 1, wherein the at least one first opticalfiber in the first cable section comprises a plurality of first opticalfibers, the at least one second optical fiber in the second cablesection comprises a plurality of second optical fibers, and the methodfurther comprises: binding optical fibers of an unjacketed segment ofthe plurality of first optical fibers extending beyond the first jacketwith at least one polymeric material to form a first optical fiberribbon; and binding optical fibers of an unjacketed segment of theplurality of second optical fibers extending beyond the second jacketwith the at least one polymeric material to form a second optical fiberribbon; wherein the fusion splicing comprises mass fusion splicingbetween ends of optical fibers of the first optical fiber ribbon andends of optical fibers of the second optical fiber ribbon, and the atleast one splice joint comprises a plurality of splice joints.
 8. Themethod according to claim 1, wherein: the binding of the optical fibersof the unjacketed segment of the plurality of first optical fiberscomprises contacting the plurality of first optical fibers with the atleast one polymeric material in a flowable state and solidifying the atleast one polymeric material to form the first optical fiber ribbon; andthe binding of the optical fibers of the unjacketed segment of theplurality of second optical fibers comprises contacting the plurality ofsecond optical fibers with the at least one polymeric material in aflowable state and solidifying the at least one polymeric material toform the second optical fiber ribbon.
 9. The method according to claim1, wherein: each optical fiber of the pluralities of first and secondoptical fibers comprises a stripped portion proximate to the pluralityof splice joints and a pre-coated portion distal from the plurality ofsplice joints; the plurality of first optical fibers, the plurality ofsecond optical fibers, and the plurality of splice joints form aplurality of spliced optical fibers; and the forming of the polymericovercoating over the at least one splice joint comprises: contacting theplurality of splice joints and at least part of the stripped portion ofeach optical fiber of the pluralities of first and second optical fiberswith the at least one polymeric material in a flowable state; alteringposition of at least some spliced optical fibers of the plurality ofspliced optical fibers to yield a configuration in which the pluralityof spliced optical fibers have a non-coplanar arrangement at the spliceregion; and solidifying the at least one polymeric material to form asolidified polymeric material with the plurality of spliced opticalfibers being in the non-coplanar arrangement at the splice region. 10.The method according to claim 1, wherein the at least one polymericmaterial in a flowable state comprises a molten polymeric material, andthe solidifying of the at least one polymeric material comprises coolingthe at least one polymeric material.
 11. The method according to claim1, further comprising applying a tubular covering member over the spliceregion, wherein the tubular covering member overlaps portions of thefirst jacket and the second jacket.
 12. An apparatus for applying athermoplastic coating over components of the fiber optic cable assemblyin the method of claim 1, the apparatus comprising: a support memberdefining a working surface; a trough arranged above the working surfaceand defining a trough cavity configured to retain a pool of moltenthermoplastic material, wherein the trough is bounded by a rear wall, afront wall, side walls, and the working surface, and wherein a lateralinsertion slot extends (i) between the working surface and the frontwall and (ii) between the working surface and at least portions of theside walls, with the lateral insertion slot being in fluid communicationwith the trough cavity; and a heating element configured to heat atleast the working surface to maintain the pool of molten thermoplasticmaterial in a molten state.
 13. The apparatus of claim 12, wherein thetrough has a trough length extending in a longitudinal directionsubstantially parallel to the front wall and the rear wall, and has atrough width extending in a lateral direction substantially parallel tothe side walls, with the trough length being greater than the troughwidth.
 14. The apparatus according to claim 12, further comprising asupport member having a longitudinal dimension, a lateral dimension, andleft and right side surfaces, wherein: the support member comprises asupport member length extending in a longitudinal direction, and asupport member width extending in a lateral direction; the supportmember defines at least one longitudinal recess having a floor that isrecessed relative to the working surface; and the at least onelongitudinal recess extends over the entire support member length topenetrate the left and right side surfaces.
 15. The apparatus accordingto claim 12, wherein the at least one longitudinal recess comprises aplurality of longitudinal recesses, and each longitudinal recess of theplurality of longitudinal recesses comprises a different width.
 16. Theapparatus according to claim 12, further comprising a body structurecontaining the heating element, wherein the body structure is configuredto transfer heat from the heating element to the support member and theworking surface by thermal conduction.
 17. The apparatus according toclaim 12, wherein the heating element comprises a resistive heatingelement.